Move to yaml-based configuration

This commit updates the configuration to be yaml-based and updates the
configuration to read in a yaml file.

internal/config/validators/duration.go

@@ -0,0 +1,14 @@
+package validators
+
+import "time"
+
+func ValidateDuration(d *time.Duration, dflt string) error {
+	if *d == 0 {
+		var err error
+		*d, err = time.ParseDuration(dflt)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}